Positive sealing for hydraulic hose adapters of the male to female type is known to be through metal to metal contact between male and female members, in particularly relevant cases, along a 12, 30, 37 or 45 degree frustoconical surface thereof See, Klaes, J., Hydraulics & Pneumatics, "How to Identify International High-Pressure Hydraulic Couplings," January, 1990. Problems are known to exist in such systems, to include torquing, casual damage, high pressure leaks, and vibration, which result in damaged adapters and leakage.
An alternate modification is the so-called flat face O-ring seal (FFOR). The FFOR has its male part made with a flat face, rather than a conical face, and a circumferential groove is machined in the face. An O-ring is installed in the groove. The corresponding FFOR female end required a flat face stub end to be brazed to it. See, Klaes, supra., SAE J1453. The FFOR, while successful in eliminating leaks, is not cost effective to manufacture, is difficult to repair in the field due to the brazing requirement, has a continual problem of loose O-rings, which fall out, and there is no appreciative vibration dampening provided the system.
In 1985, U.S. Pat. No. 4,458,926 was issued to Williamson, for a hydraulic hose adapter with an O-ring seal. See also, corresponding Canadian Patent 1,251,237. Therein, an O-ring groove is machined in the tail of a male 37 or 45 degree JIC or SAE taper. This was an improvement over the FFOR seal in cost, but other problems still remained. The groove at the tail of the 37 or 45 degree taper weakens the fitting, and it cannot be effectively made in sizes under 3/8 of an inch. Damage to the O-ring groove can impair its ability to seal. Moreover, O-rings depend on pressure to help seal, and so, an under torqued condition combined with low pressure can engender leaks. In addition, that O-ring seal invention does not adequately address the vibration problems inherent in most hydraulic systems, and such vibration is a major cause of leakage in hydraulic systems.